For measuring the concentration of trace quantity of oxygen in an industrial gas such as nitrogen, hydrogen, argon or helium, the luminous reaction between oxygen and yellow phosphorus vapor is employed. The intensity of light generated by the reaction is measured by a photodetector such as a photomultiplier. The yellow phosphorus vapor is conventionally obtained by the sublimation of solid yellow phosphorus at room temperature (15.degree.-25.degree. C.).
A method and an apparatus for measuring trace quantity of oxygen in a gas using the yellow phosphorus vapor are described in, for example, Japanese Laid Open Patent Application (Kokai) No. 63-302348. These will now be described referring to FIGS. 7 and 8.
An apparatus for measuring trace quantity of oxygen in a gas shown in FIG. 7 comprises a reaction chamber 10, a sample gas supplying duct 11 for supplying the sample gas to the reaction chamber 10, a yellow phosphorus vapor supplying duct 13 for supplying the yellow phosphorus vapor to the reaction chamber 10, which is generated from solid phosphorus P contained in a yellow phosphorus container 12, a photodetector 14 such as a photomultiplier for measuring the intensity of the light generated by the reaction between the oxygen in the sample gas and the yellow phosphorus vapor in the sample gas in the reaction chamber 10.
The quantity of oxygen in the sample gas is detected by supplying the sample gas through the sample gas supplying pipe 11 to the reaction chamber 10 and simultaneously supplying yellow phosphorus vapor generated from the solid yellow phosphorus P to the reaction chamber 10 through the yellow phosphorus vapor supplying duct 13 so as to allow a reaction between the yellow phosphorus vapor and the oxygen in the sample gas, followed by measuring the intensity of the light generated by the reaction by a photodetector 14 so as to determine the oxygen concentration based on the output from the photodetector.
An apparatus for measuring trace quantity of oxygen in a gas shown in FIG. 8 comprises a reaction chamber 15, a sample gas supplying pipe 11 for supplying the sample gas to the reaction chamber 15, a container 16 provided in the reaction chamber 15 for harboring solid yellow phosphorus P, a photodetector 14 such as a photomultiplier for measuring the intensity of light emitted by the reaction between the yellow phosphorus vapor and the oxygen in the sample gas.
The quantity of oxygen in the sample gas is measured by reacting the yellow phosphorus vapor sublimated in the reaction chamber 15 and the oxygen in the sample gas so as to emit light, and by measuring the intensity of the light emitted by the reaction.
However, in the application fields of industrial gases, for example, in the field of semiconductor, it is demanded to accurately determine the oxygen level in a gas to be used in the order of ppb.
Although the trace quantity of oxygen may be determined in the order of 1 ppm or less by the above-described conventional method and apparatus by controlling the amount of the yellow phosphorus, it is difficult to detect the extremely small amount of oxygen with a level of several ppb or less with high precision by the conventional method and apparatus.